Optical coherence tomography (OCT) is used to capture a high-resolution cross-sectional image of scattering biological tissues and is based on fiber-optic interferometry. An example OCT system is described in U.S. Pat. No. 5,321,501 and U.S. Patent Application Publication No. 2009/0198125 which are incorporated by reference herein in its entirety. The core of an OCT system is a Michelson interferometer, wherein a first optical fiber is used as a reference arm and a second optical fiber is used as a sample arm. The sample arm includes the sample to be analyzed, as well as a small probe that contains small optical components therein. An upstream light source provides the imaging light. A photodetector is arranged in the optical path downstream of the sample and reference arms. The probe is used to direct light into or onto the sample and then to collect scattered light from the sample.
Optical interference of light from the sample arm and the reference arm is detected by the photodetector only when the optical path difference between the two arms is within the coherence length of the light from the light source. Depth information from the sample is acquired by axially varying the optical path length of the reference arm and detecting the interference between light from the reference arm and scattered light from the sample arm. A three-dimensional image is obtained by transversely scanning in two dimensions the optical path in the sample arm. The axial/depth resolution of the process is determined by the coherence length, while the overall transverse resolution is dictated by the size of the image spot formed by the optical components of the probe.
Because the probe typically needs to be inserted into a small cavity of the body, it must be small and preferably have a simple optical design. Example designs for the probe include a transparent cylinder in which the miniature probe optical components are contained and through which light is transmitted and received. However, the curved body of the transparent cylinder induces optical aberrations that, if uncorrected, can degrade the image quality to the point where the image is useless. Moreover, having multiple and separate optical components in the probe is problematic because the small optical components have to be assembled and aligned, which adds to the cost and complexity of manufacturing the probe.